1. Field of the Invention
The present invention relates to a chemical mechanical polishing apparatus that is used for manufacturing semiconductor devices. In particular, the present invention relates to a polishing adjustment of a polishing pad using a dresser.
2. Description of Related Art
FIGS. 9A-9D show drawings for explaining the prior art. A state in which a polishing pad 102 is dressed is shown. As shown in FIG. 9A, a dresser 103 is placed on a polishing pad 102 that is adhered onto a surface plate 101. When a pressure is applied to the dresser 103, the surface of the polishing pad 102 is ground by a diamond particle surface 103A formed on the peripheral surface zone of the dresser 103. As a result, the surface of the polishing pad 102 is polished as shown in FIG. 9A. In general, an abrasive material or pure water is supplied to the polishing pad during a dressing process.
Polishing is carried out in a planarization process during manufacturing of a semiconductor device or the like. During such polishing, however, the abrasive material and/or polishing dust sticks to the surface of the polishing pad 102, which eventually causes the polishing process to become unstable. For this reason, in order to maintain stable polishing, the polishing pad 102 needs to be dressed and polished by the dresser 103.
However, the above-described prior art has the following problem. As shown in FIGS. 9B and 9C, the grind amount of the portion of the polishing pad 102 at distance Rt from the center of rotation of the surface plate 101 is proportional to the contact length L of the diamond particle surface 103A, with the polishing pad 102 at distance Rt from the center of the surface plate 101. By a simple calculation, the length L is given by
L=2xc2x7Rtxc2x7(Cosxe2x88x921((Rt2+Rx2xe2x88x92R12)/(2xc2x7Rtxc2x7Rx))xe2x88x92Cosxe2x88x921((Rt2+Rx2xe2x88x92R22)/(2xc2x7Rtxc2x7Rx))xe2x80x83xe2x80x83(1)
Here, as shown in FIGS. 9B and 9C,
Rx: the distance between the center of the dresser 103 and the center of the surface plate 101;
R1: the outside radius of the diamond particle surface 103A; and
R2: the inside radius of the diamond particle surface 103A.
FIG. 11 shows the dependency of the contact length L of the diamond particle surface 103A with the surface of the polishing pad 102 at distance Rt from the center of the surface plate 101 when, for example, Rx=17 cm, R1=16 cm, and R2=15.5 cm. The graph shows that the length L varies over a wide range within the polishing pad. Since the grind amount of the polishing pad 102 is proportional to the length L, the grind amount of the polishing pad 102 varies over a wide range. As a result, the surface of the polishing pad 102 cannot be made flat as needed. The minimum grind amount required to achieve a satisfactory state of polishing is pre-determined. Therefore, even at a location where the value of L is the smallest, the required minimum grind amount must be secured. On the other hand, at a location where the value of L is large, the polishing pad is over-ground.
As discussed above, the value of L grows very large in a region near the periphery of the surface plate (at points 29 cm from the center of the surface plate) and in a region near the center of the surface plate (at points 1.5 cm from the center of the surface plate). Therefore, in these regions, the polishing pad is ground by a large amount. The problem that the polishing pad is ground by a large amount in a region near the periphery of the surface plate can be solved by increasing the diameter of the dresser 103. FIG. 12 shows the dependency of L on the distance Rt from the center of the surface plate 101 in case the diameter of the dresser 103 has been increased to Rx=20 cm, R1=19 cm, and R2=18.5 cm. In this case, as seen from FIG. 12, the value of L is 1.47 cm at the point where Rt=29 cm, which is shorter by 2.1 cm than the value of L at the point where Rt=29 cm in the case shown in FIG. 11. However, in the interior of the admissible range, the value of L achieves a maximum of 2.44 cm at the point where Rt=1.5 cm, which is not significantly smaller than the maximum value of L achieved at Rt=1.5 cm in the case shown in FIG. 11, resulting in practically no improvement at all.
Thus, in the case the grind amount of the polishing pad varies over a wide range depending on the distance Rt from the center of the surface plate 101, the life span of the polishing pad is seriously shortened. A polishing pad is dressed and ground after it has been used to polish a prescribed number of semiconductor wafers. FIG. 10 is a schematic cross sectional view of the grind surface 102A of the polishing pad 102 attached onto the polishing surface plate 101. In FIG. 10, the region 102A1 where the grind amount is the largest (position 1.5 cm from the center of the surface plate), the region 102A2 where the grind amount is the smallest (position 6.9 cm from the center of the surface plate), and the region 102A3 which is the outer limit of the admissible polishing range (position 29.0 cm from the center of the surface plate) are indicated with arrows.
As mentioned before, in order to carry out stable polishing, the polishing pad must be ground at least by a minimum necessary amount. The region 102A2, where the grind amount is the smallest (position 1.5 cm from the center of the surface plate), must also be ground at least by the same minimum necessary amount, which is 0.67 xcexcm per wafer in this case. However, in the region 102A1, where the grind amount is the largest (position 1.5 cm from the center of the surface plate), 1.67 xcexcm per wafer is ground. The life span of the polishing pad 102 is determined by the amount ground by the dressing. Therefore, if the polishing pad 102 is dressed by an excessive amount, even the surface of the polishing surface plate 101 can be ground. When this happens, the surface of the polishing surface plate 101 is damaged, and the polishing surface plate 101 needs to be replaced.
As explained above, the polishing pad 102 is ground by a large amount in the interior of the admissible polishing range even though other parts of the polishing pad 102 remain sufficiently thick within the admissible polishing range. Therefore, the polishing pad 102, which is relatively expensive among the required items for manufacturing semiconductors, needs to be replaced at an early stage. This means that the semiconductor manufacturing cost is significantly increased. Moreover, it normally takes 1 to 1.5 hours to replace a polishing pad, during which time the CMP apparatus cannot manufacture any semiconductor devices, resulting in a low operation rate. As the life span of the polishing pad 102 becomes shorter, the polishing pad 102 must be replaced more frequently, which leads to a low operation rate of the apparatus.
The present invention aims to solve the above-described problems. Therefore, it is an object of the present invention to provide a polishing apparatus having a dresser equipped with a polishing pad and an inclined polishing particle surface for adjusting polishing. It is also an object of the present invention to provide a polishing apparatus having a dresser equipped with a polishing pad and a polishing particle surface for adjusting polishing such that a pressure for adjusting a polishing can be applied onto the polishing particle surface. This object is achieved by combinations as will be described. Further advantageous and exemplary combinations of the present invention are also described.